Japan has sent a submarine to the South China Sea for the first time since the Second World War, to participate in military exercises.
The Kuroshio last month joined the country's newest helicopter-carrying destroyer, Kaga, in combined anti-submarine warfare operations with the U.S. Navy.
For other big industrial nations with global security interests, it would barely have been worth a mention. But for Japan it was another important -- and welcome -- move in its tiptoe advance to the wider defense role that Prime Minister Shinzo Abe is resolutely pursuing.
Even as Abe, who was re-elected president of the ruling Liberal Democratic Party in September, is preparing to revise Japan's pacifist constitution, he is rightly making full use of the existing laws to defend Tokyo's interests.
Japan is extending its reach from home waters to the South China Sea, where the shipping lines are nothing less than Tokyo's energy and economic lifelines. Moreover, it is precisely where China, Japan's most significant strategic challenger, is expanding its military presence and reinforcing claims to disputed islands and maritime territory. In the latest sign of the growing tensions, Chinese and US warships almost collided on Sept. 30 in an incident in the disputed waters.
Japan is equally right to link its expanding role closely with that of the U.S., as it can only supplement the much larger and more assertive American naval forces.
Japan's increasing naval activities reflect the two allies' push for a "Free and Open Indo-Pacific" -- a political strategy that also includes India and Australia aimed at containing Chinese expansion.
The South China Sea (SCS) is an arena of growing clashes between U.S. and Chinese nuclear strategies. As the first step to improve its retaliatory nuclear strike capability against the huge American atomic arsenal, China has deployed strategic submarines in the SCS, operating from a base on Hainan Island. Maintaining anti-submarine warfare capability in the SCS to match the Chinese efforts is a key U.S. naval strategy, in which Japan plays an increasingly useful role.
China's recent challenges against U.S. and Australian naval vessels on freedom-of-navigation voyages in the SCS have lend more credibility to Japan's assessment that Beijing represents a growing strategic threat.
Japan is increasingly convinced that China treats the SCS as its territorial waters. In territorial waters, passage of even commercial vessels can be regulated during international conflicts. Even during peace time, foreign military vessels cannot freely transit such waters or conduct exercises or intelligence-gathering activities.
While China's naval expansion poses a growing military challenge to the U.S., in the first instance, it also attempts to coerce Southeast Asian states into acquiescing to Beijing's legal claims to disputed territory, for example around the Spratly Islands.
Japan has responded both diplomatically and militarily to counter the growing Chinese naval presence in the SCS. Since 2010, Tokyo has openly criticized China over the SCS dispute and called for a negotiated solution among the disputants, which include Vietnam and the Philippines.
Japan has worked with the U.S. and some Southeast Asian countries to have this issue addressed in various regional forums such as the annual East Asia Summit.
Japan has also cooperated with the littoral states of the Malacca Straits, a key maritime choke point, to ensure safe passage of commercial vessels.
Tokyo has contributed to anti-piracy activities in the region and helped develop a coast guard network that has recently expanded to Indian Ocean littoral states. Japan has provided patrol boats to Vietnam and the Philippines since 2015, though it declined a request from Manila for high-tech P3-C surveillance/anti-submarine warfare planes.
On a bigger scale, Kaga's sister ship Izumo took part in a trilateral "Malabar" naval exercise in the SCS with the U.S. and India in 2017, drilling anti-submarine warfare.
But it is worth remembering that the limited air-defense capability of the Japanese helicopter-carrying destroyers would not allow unilateral operations in the SCS in a real conflict. Even the hypothetical deployment of new F35 fighter planes on board Kaga -- currently under discussion in Tokyo -- could bring only limited gains, as China's military capacity grows with base construction in progress on disputed SCS reefs.
U.S. operations in the region -- and Japan's involvement in them -- have not deterred Beijing from preparing for deploying fighter and bomber planes. China has repeatedly protested at Japanese naval activities in the SCS.
Japan's new security activism has taken place under its pacifist constitution. A reinterpretation of Article 9 -- the key anti-militarist clause -- in 2014 to allow collective defense smoothened the way for a closer wartime cooperation with the U.S., and American allies like Australia.
Under the new interpretation, the guideline for bilateral defense cooperation with the U.S. explicitly expands the geographical scope of cooperation "beyond Asia-Pacific" and the mission scope of the Self Defense Force beyond "rear support."
While Abe is expected to present proposals to amend the constitution during his new three-year term as party president, the Kaga and Kuroshio have demonstrated that even without an amendment, Japan can increase its contribution to collective security, even far away from the home islands.
Japan is correct to increase its involvement in the SCS, as the U.S. Navy, which has for decades surrounded Japan with a sense of comfort, no longer enjoys overwhelming dominance in the light of China's naval advance.
Tokyo is supplementing both a shortage of U.S. capabilities and of credibility in the region, with increasing doubts about U.S. President Donald Trump's commitment to Asia.
Japan is also right to be cautious about cooperating with Southeast Asian states. Japan has refrained from providing sophisticated offensive military hardware, which carries multiple risks. Arms transfers may drive unintended wedges between Southeast Asian nations when their unity is essential in countering China.
There is also the risk of a country switching to China's side -- something which already appears a serious danger in the Philippines under President Rodrigo Duterte.
Japan must strike the right balance. It can seemingly expand its SCS role without the domestic political controversy involved in constitutional revision.
As long as Tokyo sticks to supplementing and anchoring the U.S. commitment to maritime security in the Indo-Pacific it will not go far wrong. Unilateral networking with local would-be partners in the SCS must proceed with caution, especially when it comes to supplying sophisticated weapons.
In this sense, the current constitution works both ways -- it allows for strengthening cooperation with the U.S. and its allies, whilst preventing Tokyo from seeking risky casual tie-ups with potentially unpredictable local partners.
Yoichiro Sato is a professor at Ritsumeikan Asia Pacific University.